Ferritic steel for high temperature use



United @tates Patent FERRITIC STEEL FOR HIGH TElVlPERATURE USE Geoffrey T. Harris, Shefiield, and Henry Cave Child, Rotherharn, England, assignors to The Birmingham Small Arms Company Limited, Birmingham, England, a British company No Drawing. Application February 17, 1956 Serial No. 566,079

Claims priority, application Great Britain February 28, 1955 12 Claims. (Cl. 75-124) This invention relates to hardenable ferritic or martensitic (i. e. non-austenitic) chromium alloy steels.

Such alloy steels have been used to a large extent in recent years for creep-resistant applications, but there is a continual demand for improved creep strength.

Examples of development in this field are to be found in British Patents Nos. 638,110, 658,115, 730,272 and 733,146. It is known that in alloys of the kind in question containing from about 9% to about 20% chromium, additions of one or more of molybdenum, tungsten, vanadium, niobium or titanium are necessary if optimum creep strength is to be developed and that for most practical purposes the carbon content should preferably not exceed 0.3%. Under these conditions the alloy tends to become non-hardenable due to the additions of ferrite stabilisers which cause the alloy to have a high percentage of ferrite under equilibrium conditions at the hardening temperature (1050-1250 C.).

The present invention provides means for maintaining hardenability while at the same time providing a comparatively high degree of creep strength.

It is known that nitrogen is an exceedingly potent stabiliser of austenite at 1050 -l250 C. causing suppression of the formation of ferrite under equilibrium conditions. However, the amount of nitrogen, which may be safely introduced into such steels is only about 0.06 0.10%, the larger additions only being feasible at the higher end of the chromium range of 9-20%. Higher nitrogen additions are in excess of solubility and cause the steel to outgas vigorously on solidification, which causes unsound ingots.

The basis of the present invention is the incorporation of specified proportions of aluminium in nitrogen-containing alloys of the kind in question. One of the efiects of the presence of aluminium is that it permits an increase in the percentage of nitrogen which may safely be added to the alloy. Although in most cases increased nitrogen will be desirable, in some cases it may be sufficient to employ normal amounts of nitrogen while still retaining the presence of aluminium. The alloys according to this invention can be free from ferrite at the hardening temperature, although containing substantial quantities of one or more of molybdenum, tungsten, vanadium and titanium and are accordingly of excellent creep resistance, that is to say, having a creep strength of at least 30 tons per square inch at 500 C., based on a creep strain of 0.1% in 100 hours.

According to one feature the invention comprises alloys within the following ranges, the percentages being by weight:

Percent Carbon 0.05- 0.3 Manganese 0.1- 4

2,848,323 Q6 Patented Aug. 19, 1958 A more restricted range of alloys according to the invention comprises:

Percent Carbon .08- .25 Manganese 0.5- 1.5 Silicon 0.3- 0.7 Chromium 9- l3 Tungsten 0 l Molybdenum 0.4- 1.0 Vanadium 0.1- 0.5 Niobium and/or tantalum 0.2- 0.7 Titanium 0- 0.5 Nickel 0- 0.5 Nitrogen 0.050.15 Aluminium 0.05-0.15 Boron O0.03 Iron and impurities Balance A still more restricted range comprises:

Percent Carbon 0.08 .25 Manganese 0.5 1.5 Silicon 0.3- 0.7 Chromium 9- 13 Tungsten 0.7- 2 Molybdenum 0.7- 2 Vanadium 0- 1 Niobium and/or tantalum 0- 1 Titanium 0- 0.5 Nickel O- 1.0 Nitrogen 0.050.15 Aluminium 0.050.15 Boron 00.03 Cobalt 2 10 Copper 0- 1.0 Iron and impurities Balance Examples of alloys according to the present invention are as follows:

Further examples of alloys according to the present invention are as follows:

Carbon lv ianganesa Molybdenum. Vanadium. Niobium Balance Balunc Iron and Impurities Further examples of alloys according to the present invention are as follows:

What we claim is: 1. Alloys comprising the following ingredients within the ranges specified:

Percent Carbon 0.05-0.3 Manganese 0.1- 4 Silicon 0.1- 4 Chromium 9- 20 At least one metal of the group consisting of tungsten and molybdenum 0.5-1O At least one metal of the group consisting of niobium and tantalum, when present 2 Vanadium, when present up to 2 Titanium, when present up to2 Nitrogen 0.05-0.33 Aluminium 0.05- 2 Boron, when present up to 0.05 Nickel, when present upto 5 Cobalt, when present up to Copper, when present up to 5 Iron and impurities Balance 2. Alloys comprising the following ingredients within the ranges specified:

Iron and impurities Balance 4 3. Alloys comprising the following ingredients Within the ranges specified:

Percent Carbon 0.08-0.25 Manganese 0.5- 1.5 Silicon 0.3- 0.7 Chromium 9- 13 Tungsten 0.7- 2 Molybdenum 0.7- 2 Vanadium, when present up to 1 At least one metal of the group consisting of niobium and tantalum, when present up to 1 Titanium, when present up to 0.5 Nickel, when present up to l Nitrogen 0.05-0.15 Aluminium 0.05-0.15 Boron, when present up to 0.03 Cobalt 2- 10 Copper, when present up to 1 Iron and impurities Balance 4. An alloy comprising:

Percent Carbon 0.08 Manganese 0.8 Silicon 0.3

Chromium 11 Molybdenum 0.5 Vanadium 0.2 Niobium 0.4

Boron 0.01 Nitrogen 0.1 Aluminium 0.2 Iron and impurities Balance 5. An alloy comprising:

Percent Carbon 0.1 Manganese 0.8 Silicon 0.4 Chromium 11 Tungsten 0.2 Molybdenum 0.5 Vanadium 0.2 Niobium 0.4

Boron 0.01

Nitrogen 0.1'25 Aluminium 0.1 Nickel 0.6 Iron and impurities Balance 6. An alloy comprising:

' Percent Carbon 0.12 Manganese 0.8 Silicon 0.4. Chromium 10.5

Cobalt 2.5 Tungsten 0.7 Molybdenum 0.7 Vanadium 0.7 Niobium 0.4 Boron 0.01 Nitrogen 0.1 Aluminium 0.05 Iron and impurities Balance 7. An alloy comprising:

Percent Carbon 0112 Manganese 0.8 Silicon 0.4 Chromium 10,5 Cobalt 2.5 Tungsten 0.7 Molybdenum 0.7 Vanadium 0.7

, Percent Niobium 0.4 Boron 0.01 Nitrogen 0.1 Aluminium 0.1 Iron and impurities Balance 8. An alloy comprising:

Percent Carbon 0.12 Manganese 1.2 Silicon 0.35 Chromium 10.5 Cobalt 2.5 Tungsten 0.8 Molybdenum 0.8 Vanadium 0.5 Niobium 0.45 Boron 0.01 Nitrogen 0.08 Aluminium 0.1 Nickel 0.6 Iron and impurities Balance 9. An alloy comprising:

Percent Carbon 0.12 Manganese 1.3 Silicon 0.3 Chromium 10.5 Cobalt 5 Tungsten 1 Molybdenum 1 Vanadium 0.45 Niobium 0.45 Boron 0.01 Nitrogen 0.15 Aluminium 0.5 Iron and impurities Balance 10. An alloy comprising:

Percent Carbon 0.12 Manganese 1.3 Silicon 0.3 Chromium 10.5 Cobalt 5 Tungsten 1 Molybdenum 1 Percent Vanadium 0.45 Niobium 0.45 Boron 0.02 Nitrogen 0.065 Aluminium 0.05 Nickel 0.8 Iron and impurities Balance 11. An alloy comprising:

Percent Carbon 0.12 Manganese 1.3 Silicon v 0.3 Chromium 10.5 Cobalt 2.2 Tungsten 1 Molybdenum 1 Vanadium 0.45 Niobium 0.45 Boron 0.02 Nitrogen 0.065 Aluminium 0.05 Nickel 1.7 Iron and impurities Balance 12. An 'alloy comprising:

Percent Carbon 0.07 Manganese 1.3 Silicon 0.3 Chromium 10.5 Cobalt 10 Tungsten 1 Molybdenum 1 Vanadium 0.45 Niobium 0.45 Nitrogen 0.065 Aluminium 0.05 Iron and impurities Balance References Cited in the file of this patent UNITED STATES PATENTS 2,736,649 Phillips Feb. 28, 1956 2,737,455 Kirkby Mar. 6, 1956 FOREIGN PATENTS 970,873 France Jan. 10, 1951 

1. ALLOYS COMPRISING THE FOLLOWING INGREDIENTS WITHIN THE RANGES SPECIFIED: 